1. Field of the Invention
The present invention relates to an ultrasonic probe which is used in an ultrasonic diagnostic apparatus which is arranged to transmit and receive ultrasonic waves into and from an organ for the purpose of obtaining information required for a medical diagnosis, and more particularly, to an ultrasonic probe which enables high-speed sector scanning of an ultrasonic beam by a mechanical means.
2. Description of the Prior Art
Mechanical sector-scanning ultrasonic probes (hereinafter referred to as "MSPs") have heretofore been widely used and are capable of providing high-quality sectoral ultrasonic tomograms (hereinafter referred to as "B-mode information") at a relatively low cost. However, from the clinical viewpoint, a strong demand exists for a diagnosis with simultaneous reference to B-mode information and also M-mode or Doppler mode information. However, prior-art MSPs have been limited in terms of their construction or operating principles.
In order to meet this demand, a certain type of MSP has recently been proposed which comprises a construction such as that disclosed in the specification of Japanese Utility Model Unexamined Publication No. 66144/1984. This conventional type of MSP will be described below with reference to FIGS. 1(a) and 1(B). In FIGS. 1(A) and 1(B), reference numeral 101 denotes a B-mode oscillator, reference numeral 102 a frame-shaped M-mode oscillator which is disposed around the B-mode oscillator 101, reference numeral 103 a rotating shaft of the B-mode oscillator 101, and reference numeral 104 a rotating shaft of the M-mode oscillator 102.
According to this arrangement, the B-mode oscillator 101 is rotated at high speed to thereby obtain B-mode information within a predetermined angular range. Simultaneously, the M-mode oscillator 102 is rotated in a desired direction by manual or electrical operations so as to obtain M-mode information. The center frequency inherent in the B-mode oscillator 101 is set so as to differ from that inherent in the M-mode oscillator 102. Therefore, even if the B-mode oscillator 101 and the M-mode oscillator 102 are actuated at the same time, neither of the oscillators can exert any influence on the information obtained by the other.
However, the above-described construction upon which the prior art relies involves the following disadvantages.
In general, if B-mode information and M-mode information are to be obtained simultaneously, M-mode information is considered to be the primary item in terms of clinical applications, while B-mode information is used as an auxiliary item for facilitating detection of a portion covered by M-mode information. Nevertheless, in terms of the configuration of the M-mode oscillator 102, the ultrasonic beams transmitted and received by the oscillator 102 have abnormally high side-lobe levels, when compared with those transmitted and received by the B-mode oscillator 101. It is said that such side-lobe levels result in one of the causes which give rise to "artifacts" causing an erroneous diagnosis. As will be evident from the above description, it is not advisable to use the oscillator 101 for the collection of B-mode information while using the oscillator 102 for the collection of the M-mode information. As mentioned above, the center frequencies inherent in the oscillators 101 and 102 are set so as to differ from each other. Hence, if either one of high-quality B-mode information and M-mode information is to be obtained at a frequency suitable for a diagnosis, another MSP is needed. This is disadvantageous from the viewpoint of economy and clinical application.